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The Scientific World Journal
Volume 2012, Article ID 185942, 25 pages
http://dx.doi.org/10.1100/2012/185942
Review Article

Current View on Phytoplasma Genomes and Encoded Metabolism

1Department of Crop and Animal Sciences, Humboldt-University of Berlin, Lentzeallee 55/57, 14195 Berlin, Germany
2Max Planck Institute for Molecular Genetics, Ihnestr. 63, 14195 Berlin, Germany
3Department of Plant Pathology, Institute of Pesticides and Environmental Protection, Banatska 31b, P.O. Box 163, 11080 Belgrade, Serbia
4Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky Straße 9-11, 26111 Oldenburg, Germany
5Department for Microbiology, MaxPlanck Institute for Marine Microbiology, Celsiusstraße 1, 28359 Bremen, Germany
6Institute for Plant Protection in Fruit Crops and Viticulture, Federal Research Centre for Cultivated Plants, Schwabenheimer Straße 101, 69221 Dossenheim, Germany

Received 26 October 2011; Accepted 20 November 2011

Academic Editors: M. J. Paul and T. Tanisaka

Copyright © 2012 Michael Kube et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Phytoplasmas are specialised bacteria that are obligate parasites of plant phloem tissue and insects. These bacteria have resisted all attempts of cell-free cultivation. Genome research is of particular importance to analyse the genetic endowment of such bacteria. Here we review the gene content of the four completely sequenced ‘Candidatus Phytoplasma’ genomes that include those of ‘Ca. P. asteris’ strains OY-M and AY-WB, ‘Ca. P. australiense,’ and ‘Ca. P. mali’. These genomes are characterized by chromosome condensation resulting in sizes below 900 kb and a G + C content of less than 28%. Evolutionary adaption of the phytoplasmas to nutrient-rich environments resulted in losses of genetic modules and increased host dependency highlighted by the transport systems and limited metabolic repertoire. On the other hand, duplication and integration events enlarged the chromosomes and contribute to genome instability. Present differences in the content of membrane and secreted proteins reflect the host adaptation in the phytoplasma strains. General differences are obvious between different phylogenetic subgroups. ‘Ca. P. mali’ is separated from the other strains by its deviating chromosome organization, the genetic repertoire for recombination and excision repair of nucleotides or the loss of the complete energy-yielding part of the glycolysis. Apart from these differences, comparative analysis exemplified that all four phytoplasmas are likely to encode an alternative pathway to generate pyruvate and ATP.